Insights into high entropy ceramics under extreme conditions: Ablation behavior and microstructure evolution of C/C-(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C composites

High entropy ceramics (HECs) exhibit superior oxidation/ablation properties than traditional ceramics, particularly forming a low melting point phase with self-healing effect during the ablation process. Herein, C/C-(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C composites were fabricated by the combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI). Oxyacetylene ablation behavior of C/C-(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C composites was studied systematically under a heat flux of 2.4 MW/m², resulting in mass and linear recession rates of 0.58 mg/s and 5.13 µm/s, respectively. Due to the unique preferential behavior of multi-components, a dense transition layer containing (Hf, Zr)TiO₄ and (Nb, Ta, Ti)C was formed between the oxide layer and the matrix, which alleviated the thermal expansion coefficient mismatch between the oxide layer and the matrix, protecting the internal matrix at ultra-high temperatures. Our work investigated the ablation protection behavior and mechanism of C/C-(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C and broadened the application of HECs in the field of ultra-high temperature ablation resistance for carbon-based composites.